The present invention relates to the transporting of a sheet workpiece. More particularly this invention concerns an apparatus for cutting an end off an elongated workpiece and transporting it away from the cutting location.
In many manufacturing processes an effectively endless flexible workpiece of paper, fabric, sheet metal, or plastic film or foil is fed discontinuously in an input direction to a cutting station where with each step or advance of the workpiece a sheet is cut off its leading end. These sheets must be transported away, typically by means of a conveyor operating continuously in an output direction transverse to the input direction. As in any production operation, it is important to be able to carry out the cutting and carrying-off operations as quickly as possible without of course damage to the workpiece.
This is typically done by gripping the leading end of the workpiece by a transporter/gripper and then cutting it free of the discontinuously arriving web workpiece. Then the gripper is moved up or down to an output level and loads the cut-off sheet into an output conveyor which extends transversely away from the input location on the output level. Once the sheet workpiece is engaged by the output conveyor, the gripper releases it and returns to the input location to grip the leading end of the web workpiece and restart the process.
Before the incoming web workpiece can be advanced and a new sheet can be cut off it, the grippers that move it to the output conveyor must be back in position. In addition it is often necessary for the sheet workpiece to be moved out of the way before the grippers can be moved back up to the input station. Due to the horizontal offset of the input and output stations, the path must be completely clear for the grippers to return to their starting position.
In some systems the gripper is formed as so-called needle beams whose points engage into the workpiece and hold it such grippers can work from one side and allow the apparatus to cycle more rapidly since they can move out of the way efficiently. They damage the workpiece edges however so that they are only usable on coarse fabrics or workpieces that are going to be trimmed.
In the simplest system the input station is directly above the output station. The grippers are spaced in the input direction and extend transversely across the workpiece, perpendicular to the input transport direction. The gripper drops straight down and then moves in the output direction to insert the workpiece into the output conveyor so it can be carried off while at the same time the workpiece is advanced in the upper station to get ready for the next cycle. Then the grippers must move further in this second direction to clear the workpieces in the lower output station and upper input station before they can be raised back up and moved horizontally back in place for the next cycle. This complex movement of the grippers takes quite some time and makes the apparatus fairly complex and large, although it does have the advantage of treating the workpiece very gently.
It is therefore an object of the present invention to provide an improved apparatus for cutting a sheet off an elongated workpiece and transporting away the cut-off sheet.
A further object is to provide an improved method of operating such an apparatus.
Another object is the provision of such an improved apparatus for cutting a sheet off an elongated workpiece and transporting away the cut-off sheet which overcomes the above-given disadvantages, that is which is simple and compact, and which cycles rapidly.
An apparatus for cutting sheets from an elongated workpiece has according to the invention a supply for feeding a leading end of the workpiece in an input direction on an upper horizontal input plane to an input station, a device for cutting the workpiece transversely of the input direction immediately upstream in the input direction from the input station, an output conveyor defining a lower horizontal output plane below the input plane in an output station below the input station and effective in an output direction transverse to the input direction, and upper and lower grippers engageable in a closed position with the workpiece in the upper station and displaceable into the lower station. This apparatus is operated according to the invention by first closing the grippers on the workpiece leading end in the upper station and then cutting off the leading end of the workpiece to leave a sheet held in the grippers. The grippers holding the sheet are then moved downward and in the output direction to align the sheet with the output plane and pass the sheet to the output conveyor. The grippers are opened to release the cut-off sheet to the output conveyor for displacement of the sheet away in the output direction. Then the upper gripper is moved downstream in the output direction until it is out from underneath the input station. The upper gripper is moved upward to immediately above the upper plane and the lower gripper upward to immediately below the upper plane. Finally the upper gripper is moved upstream in the output direction until it is above the input station and the lower gripper is moved downstream in the output direction until it is underneath the input station. After the sheet has been moved out of the input station the leading end of the workpiece is advanced on the input plane into the input station so that the cycle can be repeated. As the upper gripper is moved downstream after handing off the workpiece, the lower gripper can be held stationary or, if necessary, can be moved oppositely upstream in the output direction until it is out from underneath the released sheet on the output conveyor.
According to the invention the output station is partially underneath and partially offset in the output direction from the input station. Thus the system can work very rapidly. The ability of the grippers to move oppositely allows them to get out of the way of whatever is blocking them from moving back to the right level and allows them to slide back over and under the new workpiece end in the upper input station to start another cycle. With this system, therefore, the input station can be reloaded while the just cut sheet is being handed off, and the grippers can get back into position without having to travel through long paths.
According to the invention each upper gripper comprises two upper gripper bars spaced apart in the input direction and jointly movable vertically and in the output direction and two lower gripper bars also spaced apart in the input direction and jointly movable vertically and in the output direction.